Various electro-optical readers have previously been developed for reading bar code symbols appearing on a label, or on a surface of a target. The bar code symbol itself is a coded pattern of indicia. Generally, the readers electro-optically transform graphic indicia of the symbols into electrical signals, which are decoded into alphanumeric characters. The resulting characters describe the target and/or some characteristic of the target with which the symbol is associated. Such characters typically comprise input data to a data processing system for applications in point-of-sale processing, inventory control, article tracking and the like.
Moving beam electro-optical readers have been disclosed, for example, in U.S. Pat. Nos. 4,251,798; 4,369,361; 4,387,297; 4,409,470; 4,760,248; and 4,896,026, and generally include a light source consisting of a gas laser or semiconductor laser for emitting a laser beam. The laser beam is optically modified, typically by a focusing optical assembly, to form a beam spot having a certain size at a predetermined target location. The laser beam is directed by a scanning component along an outgoing optical path toward a target symbol for reflection therefrom. In response to manual actuation of a physical trigger, the reader operates by repetitively scanning the laser beam in a scan pattern, for example, a line or a series of lines across the target symbol by movement of the scanning component, such as a scan mirror, disposed in the path of the laser beam. The scanning component may sweep the beam spot across the symbol, trace a scan line across and beyond the boundaries of the symbol, and/or scan a predetermined field of view.
Moving beam electro-optical readers also include a photodetector, which functions to detect laser light reflected or scattered from the symbol. In some systems, the photodetector is positioned in the reader in a return path so that it has a field of view, which extends at least across and slightly beyond the boundaries of the symbol. A portion of the laser beam reflected from the symbol is detected and converted into an analog electrical signal. A digitizer digitizes the analog signal. The digitized signal from the digitizer is then decoded by a microprocessor, based upon a specific symbology used for the symbol, into a binary data representation of the data encoded in the symbol. The binary data may then be converted into the alphanumeric characters represented by the symbol. The data may be decoded locally or sent to, and decoded in, a remote host for subsequent information retrieval.
Moving beam electro-optical readers have been used for reading one-dimensional symbols each having a row of bars and spaces spaced apart along one direction, and for processing two-dimensional symbols, such as Code 49, as well. Code 49 introduced the concept of vertically stacking a plurality of rows of bar and space patterns in a single symbol. The structure of Code 49 is described in U.S. Pat. No. 4,794,239. Another two-dimensional code structure for increasing the amount of data that can be represented or stored on a given amount of surface area is known as PDF417 and is described in U.S. Pat. No. 5,304,786.
Both one- and two-dimensional symbols can also be read by employing imaging readers. For example, a solid-state image sensor device may be employed which has a one- or two-dimensional array of cells or photosensors which correspond to image elements or pixels in a field of view of the device. In response to actuation of a physical trigger, the array captures light from the symbol. Such an image sensor device may include a one- or two-dimensional charge coupled device (CCD) or a complementary metal oxide semiconductor (CMOS) device and associated circuits for producing electronic signals corresponding to a one- or two-dimensional array of pixel information over the field of view. The electronic signals may be processed by a microprocessor either locally or sent to, and processed in, a remote host to read the symbol.
Depending upon the application, such moving beam and imaging readers can be configured in housings of various configurations, such as a gun-shaped housing typically held in the palm of the operator's hand, or a box-shaped housing that rests on a countertop to read symbols in a workstation mode, and is lifted off the countertop and aimed at the symbols to read them in a handheld mode. In parcel delivery and tracking applications, some of the components of each type of reader are mounted in one or more modules and supported on the body, neck, arm, wrist, and/or finger of a human operator, with a wired and/or wireless connection between the modules and with a base station. See, for example, U.S. Pat. Nos. 6,634,558 and 5,610,387. Such operator-supported readers are of especial benefit to parcel delivery personnel since it keeps the palms of both their hands free to pick up, hold and deliver parcels, as well as to receive delivery confirmations from recipients.
As advantageous as these readers are, experience has shown that they are unsatisfactory in some respects. For example, physical triggers are prone to breakage, especially after repeated, prolonged use. The art has proposed so-called triggerless readers that have no trigger to break, but these readers are energized all the time, thereby consuming electrical energy. This is a problem for battery-operated readers, and especially for small form factor readers of the type supported on the operator since a smaller reader has a smaller, lighter battery that has a correspondingly smaller energy capacity. Energy consumption is particularly high for an imaging reader since it typically requires an illuminator comprised of multiple light sources to illuminate the field of view during image capture.
Also, the imaging reader must be held in a substantially stationary position relative to the symbol during image capture. Only when the imaging imager is held in a substantially fixed position relative to the symbol can an image of the symbol be clearly captured and decoded, with the data encoded in the symbol being sent to a host for processing. Operators who are hurried, for example, delivery personnel, may swipe the symbol across a window of the reader, sometimes once, sometimes several times, or may present the symbol to the reader with a component of motion relative to the window, either toward and away from the window, and/or side-to-side across the window, and/or up-and-down relative to the window, thereby blurring the image of the symbol due to the relative motion between the symbol and the imager and, as a result, the image cannot be reliably and successfully decoded and read.